At a fully mechanized working face of a coal mine as prototype,we investigated,by simulation,the flow field and dust distribution during the process of its isolation by a curtain of air,using the CFD software, Fluent....At a fully mechanized working face of a coal mine as prototype,we investigated,by simulation,the flow field and dust distribution during the process of its isolation by a curtain of air,using the CFD software, Fluent.The results show that the air curtain installed on the shearer can effectively prevent the dust （especially the respirable dust）from diffusing into the work area of the operator,reducing the dust concentration on the side of the operator and greatly improving his working environment.The field application of the air curtain shows that the dust-isolation effect of an air curtain is quite noticeable.The isolation efficiency for respiratory dust is over 70%and,as well,it has good dust-isolation effect for nonrespiratory dust.The air curtain is a useful way to resolve the problem of dust-isolation at a fully mechanized working face.It has a practical background elsewhere with more extensive applications.展开更多
Purpose： Physical activity （PA） and sedentary behavior （SB） are increasingly considered independent health behaviors. Additionally, current research suggests that both controlled and automatic determinants accoun...Purpose： Physical activity （PA） and sedentary behavior （SB） are increasingly considered independent health behaviors. Additionally, current research suggests that both controlled and automatic determinants account for their adoption. The purpose of this article was to identify intention-automaticity profiles toward PA and screen-based SB and to examine how those profiles are associated with different behavioral patterns. Method： Two cross-sectional studies based on self-report questionnaires were conducted with French high school students （Study 1： n = 198; Study 2： n = 185）. Results： In all, 4 distinct motivational profiles appeared. The first 3 clusters emerged in both studies： ＂PA＂ （high levels of automaticity and intention for PA, low levels of automaticity and intention for screen-based SB）; ＂screen＂ （high levels of automaticity and intention for screen-based SB, low levels of automatieity and intention for PA）, and ＂mixed＂ （high levels of all variables）, whereas the fourth cluster was observed only in Study 2： ＂high control＂ （below-mean levels of automaticity, high levels of intention toward both PA and screen-based SB）. Adolescents with a screen profile displayed the least healthy behavioral pattern, whereas those in the PA profile demonstrated the most favorable behaviors. Conclusion： Future research is needed to extend these results to other populations using complementary assessment methods of automatic psychological processes and PA and SB behaviors.2018 Published by Elsevier B.V.on behalf of Shanghai University of Sport. This is an open access article under the CC BY-NC-ND license.（http：//creativecommons.org/licenses/by-nc-nd/4.0/）.展开更多
The reflecting and transmitting effects of a planar unidirectionally conducting screen are analyzed based on the accurate closed-form expression for electric field of an arbitrarily oriented electric dipole.For a dipo...The reflecting and transmitting effects of a planar unidirectionally conducting screen are analyzed based on the accurate closed-form expression for electric field of an arbitrarily oriented electric dipole.For a dipole oriented along the wire elements of the screen,the screen acts as a perfectly electrically conducting plane.For a dipole perpendicular to the wire elements,the fields reflected by the screen can be interpreted as the contribution of an image dipole and image transmission-line current source,while the transmitted field is arisen from image transmission-line source.The expressions of related surface waves are derived and can be compared with previous results.展开更多
A combined method of numerical simulation and field testing was adopted in this study in the interest of solving the problem of hard to control high concentrate dusts on a fully mechanized mining face. In addi- tion, ...A combined method of numerical simulation and field testing was adopted in this study in the interest of solving the problem of hard to control high concentrate dusts on a fully mechanized mining face. In addi- tion, the dust suppression effect of a multi-direction whirling air curtain was studied in this paper. Under the influence of the wall attachment effect, the compressed air which blows out from the two-phase or three-phase radial outlets on the generator of the air curtain can form a multi-direction whirling air curtain, which can cover the whole roadway section of a fully mechanized mining face. The traditional method of controlling dust is a forcing system with exhaust overlap which has the major disadvantage of lacking a jet effect and consequently results in poor dust control. It is difficult to form the air flow field within the range of Lp ≤ 5√S. However, due to the effect of this novel system, the radial airflow can be turned into axial airflow allowing fresh air to flow through the length of the heading. The air flow field which is good at controlling dust diffusion can be formed 12.8 m from the heading face. Furthermore, the field measurement results show that before the application of a multi-direction whirling air curtain, the dust concentration is 348.6 mg/m^3 and 271.4 mg/m^3 respectively at the roadway cross-section measurement points which are 5 m and 10 m from the heading face. However, after the application of the multi-direction whirling air curtain, the dust concentration is only 61.2 mg/m3 and 14.8 mg/m^3, respectively. Therefore, the dust control effect of a multi-direction whirling air curtain is obvious.展开更多
The effect of screen length on the screening efficiency of particles is studied under various single parameter conditions including frequency, amplitude, vibration angle, and screen inclination. The Discrete Element M...The effect of screen length on the screening efficiency of particles is studied under various single parameter conditions including frequency, amplitude, vibration angle, and screen inclination. The Discrete Element Method (DEM) has been used to simulate the screening process. A functional relationship between screening efficiency and screen length is established. It is shown that screening efficiency and screen length have a complicated exponential relationship. Relationships between them are profoundly discussed and conclusions are easily drawn: low values of the parameters do not benefit screening; screening efficiency generally increases with screen length; screening efficiency reaches a plateau when these parameters are in range frequently encountered in practical applications.展开更多
基金Financial support for this work,provided by the National Natural Science Foundation of China(No.50974060)the State Safety Production Science and Technology Development Plan (No.06-396)
文摘At a fully mechanized working face of a coal mine as prototype,we investigated,by simulation,the flow field and dust distribution during the process of its isolation by a curtain of air,using the CFD software, Fluent.The results show that the air curtain installed on the shearer can effectively prevent the dust （especially the respirable dust）from diffusing into the work area of the operator,reducing the dust concentration on the side of the operator and greatly improving his working environment.The field application of the air curtain shows that the dust-isolation effect of an air curtain is quite noticeable.The isolation efficiency for respiratory dust is over 70%and,as well,it has good dust-isolation effect for nonrespiratory dust.The air curtain is a useful way to resolve the problem of dust-isolation at a fully mechanized working face.It has a practical background elsewhere with more extensive applications.
文摘Purpose： Physical activity （PA） and sedentary behavior （SB） are increasingly considered independent health behaviors. Additionally, current research suggests that both controlled and automatic determinants account for their adoption. The purpose of this article was to identify intention-automaticity profiles toward PA and screen-based SB and to examine how those profiles are associated with different behavioral patterns. Method： Two cross-sectional studies based on self-report questionnaires were conducted with French high school students （Study 1： n = 198; Study 2： n = 185）. Results： In all, 4 distinct motivational profiles appeared. The first 3 clusters emerged in both studies： ＂PA＂ （high levels of automaticity and intention for PA, low levels of automaticity and intention for screen-based SB）; ＂screen＂ （high levels of automaticity and intention for screen-based SB, low levels of automatieity and intention for PA）, and ＂mixed＂ （high levels of all variables）, whereas the fourth cluster was observed only in Study 2： ＂high control＂ （below-mean levels of automaticity, high levels of intention toward both PA and screen-based SB）. Adolescents with a screen profile displayed the least healthy behavioral pattern, whereas those in the PA profile demonstrated the most favorable behaviors. Conclusion： Future research is needed to extend these results to other populations using complementary assessment methods of automatic psychological processes and PA and SB behaviors.2018 Published by Elsevier B.V.on behalf of Shanghai University of Sport. This is an open access article under the CC BY-NC-ND license.（http：//creativecommons.org/licenses/by-nc-nd/4.0/）.
文摘The reflecting and transmitting effects of a planar unidirectionally conducting screen are analyzed based on the accurate closed-form expression for electric field of an arbitrarily oriented electric dipole.For a dipole oriented along the wire elements of the screen,the screen acts as a perfectly electrically conducting plane.For a dipole perpendicular to the wire elements,the fields reflected by the screen can be interpreted as the contribution of an image dipole and image transmission-line current source,while the transmitted field is arisen from image transmission-line source.The expressions of related surface waves are derived and can be compared with previous results.
基金supported by the Key Program of the Coal Joint Funds of the National Natural Science Foundation of China (No.U1261205)the Youth Program of National Natural Science Foundation of China (No.51404147)+2 种基金the Class General Financial Grant from the China Postdoctoral Science Foundation (No.2015M570601)the Scientific Research Foundation of Shandong University of Science and Technology for Recruited Talents (No.2014RCJJ029)the State Key Laboratory of Mining Disaster Prevention and Control Co-founded by Shandong Province and the Ministry of Science and Technology,Shandong University of Science and Technology (No.MDPC2013ZR02)
文摘A combined method of numerical simulation and field testing was adopted in this study in the interest of solving the problem of hard to control high concentrate dusts on a fully mechanized mining face. In addi- tion, the dust suppression effect of a multi-direction whirling air curtain was studied in this paper. Under the influence of the wall attachment effect, the compressed air which blows out from the two-phase or three-phase radial outlets on the generator of the air curtain can form a multi-direction whirling air curtain, which can cover the whole roadway section of a fully mechanized mining face. The traditional method of controlling dust is a forcing system with exhaust overlap which has the major disadvantage of lacking a jet effect and consequently results in poor dust control. It is difficult to form the air flow field within the range of Lp ≤ 5√S. However, due to the effect of this novel system, the radial airflow can be turned into axial airflow allowing fresh air to flow through the length of the heading. The air flow field which is good at controlling dust diffusion can be formed 12.8 m from the heading face. Furthermore, the field measurement results show that before the application of a multi-direction whirling air curtain, the dust concentration is 348.6 mg/m^3 and 271.4 mg/m^3 respectively at the roadway cross-section measurement points which are 5 m and 10 m from the heading face. However, after the application of the multi-direction whirling air curtain, the dust concentration is only 61.2 mg/m3 and 14.8 mg/m^3, respectively. Therefore, the dust control effect of a multi-direction whirling air curtain is obvious.
基金the Special Topic Fund of Key Science and Technology of Fujian Province (No.2006HZ0002-2) for the financial support of these studies
文摘The effect of screen length on the screening efficiency of particles is studied under various single parameter conditions including frequency, amplitude, vibration angle, and screen inclination. The Discrete Element Method (DEM) has been used to simulate the screening process. A functional relationship between screening efficiency and screen length is established. It is shown that screening efficiency and screen length have a complicated exponential relationship. Relationships between them are profoundly discussed and conclusions are easily drawn: low values of the parameters do not benefit screening; screening efficiency generally increases with screen length; screening efficiency reaches a plateau when these parameters are in range frequently encountered in practical applications.
